Bump prom-client from 11.1.2 to 11.1.3

[dependabot-preview]

Bumps prom-client from 11.1.2 to 11.1.3.

Changelog

Sourced from prom-client's changelog.

[11.1.3] - 2018-09-22

Changed

• Fixed performance by avoiding Object.assign on hot paths, as well as
  mutating objects when appropriate.

Commits

• ac74915 11.1.3
• 97ed179 prepare for 11.1.3
• 6674ada Mutate labels to avoid excessive object cloning. (#220)
• 24cf59a chore: add eslint-plugin-node (#221)
• See full diff in compare view

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[paulmelnikow]

Let's pin this to a specific patch version so the server will install the right one.

Ref: #1988

[dependabot-preview]

Superseded by #2316.